Check glibc version for a particular gcc compiler

Question

I have two gcc compilers installed on my system, one is gcc 4.1.2 (default) and the other is gcc 4.4.4. How can I check the libc version used by

Answer 1

gnu_get_libc_version identifies the runtime version of the GNU C Library.

If what you care about is the compile-time version (that is, the version that provided the headers in /usr/include), you should look at the macros __GLIBC__ and __GLIBC_MINOR__. These expand to positive integers, and will be defined as a side-effect of including any header file provided by the GNU C Library; this means you can include a standard header, and then use #ifdef __GLIBC__ to decide whether you can include a nonstandard header like gnu/libc-version.h.

Expanding the test program from the accepted answer:

#include 
#ifdef __GLIBC__
#include 
#endif

int
main(void)
{
#ifdef __GLIBC__
  printf("GNU libc compile-time version: %u.%u\n", __GLIBC__, __GLIBC_MINOR__);
  printf("GNU libc runtime version:      %s\n", gnu_get_libc_version());
  return 0;
#else
  puts("Not the GNU C Library");
  return 1;
#endif
}

When I compile and run this program on the computer I'm typing this answer on (which is a Mac) it prints

Not the GNU C Library

but when compiled and run on a nearby Linux box it prints

GNU libc compile-time version: 2.24
GNU libc runtime version:      2.24

Under normal circumstances, the "runtime" version could be bigger than the "compile-time" version, but never smaller. The major version number is unlikely ever to change again (the last time it changed was the "libc6 transition" in 1997).

If you would prefer a shell 'one-liner' to dump these macros, use:

echo '#include ' | gcc -xc - -E -dM | 
    grep -E '^#define __GLIBC(|_MINOR)__ ' | sort

The grep pattern is chosen to match only the two macros that are relevant, because there are dozens of internal macros named __GLIBC_somethingorother that you don't want to have to read through.